A diesel particulate filter is used to catch PM (particulate matter) containing dark smoke or SOF (soluble organic fraction) exhausted from an internal combustion engine such as a diesel engine or the like. However, accumulated PM causes an increase of pressure in the filter.
Therefore, to prevent an increase of pressure, a heating unit such as an electric heater is equipped around the filter to combust and remove PM so as to regenerate the filter.
Such a conventional purification apparatus for exhausted gas, however, required to switch a filter to another one while the regeneration of the filter is carried out. Every time when a certain amount of PM is deposited, it is necessary to switch between at least 2 filters to repeat catching and regeneration. Regeneration of a filter requires heating inside of the filter up to combustion temperature of PM; which in turn requires installment of a heating apparatus such as an electric heater or the like. To solve such a problem, a purification system has been proposed, where hydrocarbon adsorption zone supported zeolite, and a PM filtering zone supported an oxidation catalyst are installed at an exhaustion passage of an internal combustion engine, and as the oxidation catalyst, platinum, palladium, rhodium, cerium, copper, vanadium, iron, silver or the like is disclosed (JP-A-2002-89247).
In addition, a purification apparatus for exhaust gas from a diesel engine equipped with a filter for catching particulates from a diesel engine, a catalyst converter with high activity for injected hydrocarbon (HC) installed at the upstream for the filter, and a HC control unit which is capable of supplying a large amount of HC to the catalyst converter has been proposed (JP-A-60-43113).
Furthermore, a filter for particulates exhausted from a diesel engine, coated with a catalyst component thereon has also been proposed (U.S. Pat. No. 5,100,632A). In addition, a purification apparatus for exhaust gas from a diesel engine installed a filter which supported an oxidation catalyst at downstream of a turbo charger has been proposed. This filter catches fine particles and a fuel supplying unit to generate heat by exothermic reaction between oxygen and fuel using the oxidation catalyst has also been proposed (JP-A-05-44435). In addition, a purification system for exhaust gas from an internal combustion engine which is equipped with a diesel particulates filter of continuous regeneration type at the exhaust gas passage of the engine is proposed. In this system, accumulated particulate material is removed by regeneration mode operation, at the timing when an amount of the accumulated particulate material in the filter is equal to or more than a specified discrimination value. Furthermore, in this system, a purification system which is equipped with an estimation unit to estimate an amount of accumulated particulate material into the filter, and a control unit for limiting the maximal injection amount of fuel to an internal combustion engine, at the timing when amount of particulate material is equal to or more than a specified discrimination value, has also been proposed (JP-A-2004-108207).